Photoionization is a known technique for ionizing sample present in molecular, atomic and/or other fragmental form. Ionized molecules, atoms and/or other fragments can be detected and analyzed in sample analysis systems which utilize electric and/or magnetic fields to direct ionized sample into detectors. Ionization of sample can, for instance, provide electrons which produce a current between two plates that are maintained at different DC potentials when said sample is caused to be ionized between said plates. In addition, electric and/or magnetic field utilizing mass spectrometers can separate ionized sample based upon the mass of said ionized sample when said ionized sample is caused to flow through a present electric and/or magnetic field.
Briefly, photoionization is a process in which photons of a sufficiently short wavelength, produced by a photon production source typically termed a lamp, are caused to interact with sample to cause ionization thereof. A photon producing lamp can be achieved by filling an enclosed space with a gas such as Argon, Krypton or Xenon, which provide photons at 11.8, 10.2 and 9.5 electron-volts (ev) respectively when excited by an electric discharge, for instance. It is mentioned that enclosed spaces in lamps are typically formed from sealed quartz envelopes . It is further noted that, for instance, when Xenon gas is present at low pressures, photons with a wavelength of one-thousand-four-hundred-sixty-five (1465) Angstroms can be produced by causing an electric discharge in said gas, and when Krypton gas is present at low pressures photons at a wavelength of one-thousand-two-hundred-thirty-five (1235) Angstroms can be likewise produced and when Argon is present a wavelength of one-thousand-forty-eight (1048) Angstroms can be produced. Photons of a specified wavelength have associated therewith a certain energy related to tire frequency thereof by Planck's constant. That is: EQU ENERGY=(PLANCK'S CONSTANT).times.(FREQUENCY)
where FREQUENCY is related to the WAVELENGTH of the photons through the velocity of propagation of said photons in the present gas: EQU VELOCITY=(FREQUENCY).times.(WAVELENGTH),
where Planck's constant is 6.624 times ten-to-the-minus-thirty-forth Joule-second.
It will then be appreciated that the shorter the wavelength, the more energetic will be the produced photons. This is the case as wavelength and frequency are inversely related and energy is directly proportional to frequency. Different sample molecules, atoms and/or other fragments require photons of different energy levels to cause ionization thereof. That is, for instance, sample ionized by photons produced in a Krypton gas containing lamp might not be ionized by photons produced by a Xenon containing lamp. Stated otherwise, more energetic photons are capable of removing more tightly held electrons from sample than are less energetic photons.
With the above in mind it should be readily appearant that a multiple lamp photoionization system, each of which said multiple lamps is capable of producing photons of a wavelength which differs from the wavelenght of said other lamps, would be of utility when analysis of an unknown sample is to be undertaken. Application of relatively long wavelength photons might be first applied to said sample and detection of any produced ionization undertaken, for instance. Progressively more energetic, shorter wavelength, photons could then be applied to said sample accompanied by additional detection of produced sample ionization. Analysis of single component or multiple component samples could be performed by the technique alluded to.
A problem exists, however, in that physical separation of multiple photon production source lamps makes application of photons produced by each, to a location at which a sample is present, difficult. One solution to the problem is to cause the sample to flow past a number of photon sources. A search of Patents has provided U.S. Pat. No. 2,901,625 to Friedman et al. in which this approach is disclosed. In particular said Patent describes a tube through which a multiple component sample containing gas is caused to flow. Said multiple component sample containing gas is caused to pass between a set of spaced plates, each of which plates is held at a different DC potential, simultaneous with irradiation by photons produced in a closely situated Xenon containing lamp. Detection of any current through said set of spaced plates held at differing DC potentials is simultaneously undertaken and if present indicates the presence of electrons which result when said sample is ionized. Said multiple component sample containing gas is then caused to pass between a second set of spaced plates each of which are held at a different DC potential, simultaneous with irradiation with photons produced by a lamp containing Krypton. Detection of current flowing through said second set of spaced plates again indicates that sample ionization has occurred. It is mentioned that one identified application of the system is in measuring the relative amount of xylene in toluene as Xenon photons are capable of ionizing xylene but not toluene. While the Friedman et al. invention allows application of photons of multiple wavelengths to a sample, it requires the presence of multiple detector systems and a tube through which sample containing gas is caused to flow. This invention can then De cumbersome to practice. Other Patents which describe the presence of multiple sources of radiation are U.S. Pat. Nos. 4,762,402 to Michon et al. and 4,648,951 to Maya. Another Patent, U.S. Pat. No. 5,126,676 to Huston describes a system in which a magnesium fluoride window is present in a system which provides a single source of radiation. Said magnesium fluoride window is utilized as it is transparent to photons with wavelengths between one-hundred-twenty (120) nanometers, (i.e. twelve-hundred (1200) Angstroms), and one-thousand (1000) nanometers, (i.e. ten-thousand (10,000) Angstroms). Magnesium fluoride then is transparent to photons produced by electric discharge in Xenon, Krypton and Argon gasses.
Other Patents which describe the construction of a sample analysis system include a Patent to Fay, U.S. Pat. No. 2,943,223. An elongated hollow dielectric member with spaced electrodes therein is described. During use a sample containing gas is caused to flow through said structure between said spaced electrodes, while an electric discharge takes place. While both ends of the elongated hollow dielectric member are closed, at least one is transparent to radiation. A Patent to Braman et al, U.S. Pat. No. 3,612,686 describes a sample analysis system construction in which electrodes are placed at the ends of an elongated Pyrex brand glass or quartz capillary tube, through which elongated quartz capillary tube sample containing gas is caused to flow during use while a direct current discharge carried out between said electrodes. The electrodes can be of a wire type, or of a hollow tube design. Photon radiation produced exits through the wall of the Pyrex brand glass or quartz capillary tube and into a detector.
A Patent which describe construction of gas discharge lamps is U.S. Pat. No. Re. 33,415 to Jelic. The system therein provides that electrodes should be placed into a sealed cylindrical envelope, said spaced electrodes being oriented parallel to one another, and said electrodes having a partition therebetween. A magnesium fluoride window to allow emission of photon radiation produced in said structure by electric discharge between said electrodes is described. A Patent to Dahlquist et al., U.S. Pat. No. 3,685,911 describes a capillary arc plasma source system in which a lithium fluoride window is present to allow photon radiation produced therein to escape. Lithium fluoride is transparent to radiation with wavelengths as low as eleven-hundred (1100) Angstroms. Other Patents which describe gas discharge tubes are U.S. Pat. Nos. 3,900,237 to Marcucci, 3,390,351 to Bell and 4,001,624 to Cosco et al. A particularly interesting Patent is U.S. Pat. No. 5,062,116 to Christensen. This Patent describes a halogen-compatable high-frequency discharge apparatus. Discharge tubes formed of metal fluoride glasses, (note that glasses are amorphous), are used in apparatus for emitting high frequency laser and fluorescent light. The use of metal fluoride glasses serves to make the discharge tubes resistant to corrosion from halogen-containing gas mixtures subjected to high frequency excitation in the apparatus.
The cited Patents show that use of multiple sources of ionizing photon radiation in the analysis of samples is known. Also, while the use of magnesium or lithium fluoride as a material which is transparent to photons with wavelengths between one-hundred (100) (for lithium fluoride) of one-hundred-twenty (120) (for magnesium fluoride) nanometers and one-thousand (1000) nanometers is known, no reference of which the inventor is aware teaches that multiple sources of photon radiation should be encased in a containing structure made of machinable photon radiation transparent material such as crystaline magnesium or lithium fluoride. Were such a system available, photons of different wavelengths produced in different lamps encased at different locations in said containing machinable photon radiation transparent material could easily be applied to a sample at a fixed location without significant attenuation thereof. As well, no reference of which the inventor is aware teaches that photon producing lamps can be fabricated directly in machinable photon radiation transparent material such as crystaline magnesium or lithium fluoride with said machinable photon radiation transparent material serving to directly contain gas pumped into evacuated cavities which are machined thereinto. A need is thus identified.